Original Article
Development and validation of a scoring system for the identification of pleural exudates of cardiac origin

https://doi.org/10.1016/j.ejim.2017.11.008Get rights and content

Highlights

  • Light's criteria miscategorize about 30% of cardiac effusions as “exudates”.

  • A simple scoring system accurately identify these false cardiac exudates.

  • The new scoring system is applicable when natriuretic peptide data are lacking.

Abstract

Background

Light's criteria misclassify about 30% of cardiac effusions as exudates, possibly leading to unnecessary testing. Our purpose was to derive and validate a scoring model to effectively identify these falsely categorized cardiac effusions, in the setting of natriuretic peptide lacking data.

Methods

We retrospectively analyzed data from 3182 patients with exudative pleural effusions based on Light's criteria, of whom 276 had heart failure (derivation set). A scoring model was generated with those variables identified as independent predictors of cardiac effusions in a logistic regression analysis, and further evaluated in an independent population of 1165 patients.

Results

The score consisted of age ≥ 75 years (3 points), albumin gradient > 1.2 g/dL (3 points), pleural fluid lactate dehydrogenase < 250 U/L (2 points), bilateral effusions on chest radiograph (2 points), and protein gradient > 2.5 g/dL (1 point). At the best cutoff of ≥ 7 points, the score yielded 92% diagnostic accuracy, a likelihood ratio positive of 12.7 and a likelihood ratio negative of 0.39 for labeling cardiac effusions in the derivation sample. The respective figures in the validation sample were 87%, 6.5 and 0.33. Notably, the score had higher discriminatory properties than protein and albumin gradients in both the derivation (respective area under the curve – AUC – of 0.925, 0.825, and 0.801) and validation (respective AUC of 0.908 0.862 and 0.802; all p  0.01) cohorts.

Conclusions

A simple scoring system can assist clinicians in accurately identifying false cardiac exudates when natriuretic peptides are not available.

Introduction

Pleural effusions are common in patients with decompensated heart failure (HF). The identification of cardiac effusions is usually considered to be an easy task and the performance of a pleural tap is unnecessary in most clinical situations. However, the diagnosis of cardiac effusions is not always straightforward, even when pleural fluid data are available [6]. For example, one study called into question the physicians' ability to correctly identify transudates prior to thoracentesis by showing that the initial clinical presumption failed 44% of the time [13]. In addition, Light's criteria [4], which are considered the gold standard for transudate-exudate differentiation in every-day practice, leave nearly 30% of cardiac effusions erroneously labeled as exudates [1], [10]. No consensus exists on the best way to reclassify the latter as true transudates [7]. Although the identification of cardiac effusions, in general, and false cardiac exudates, in particular, may be greatly improved with the measurement of natriuretic peptides [9], these biomarkers of HF are not always used as an initial diagnostic test for the work-up of pleural effusions and variabilities in laboratory methodologies and proper cutoffs should be considered.

The goal of this study was to provide a practical tool based on the combination of simple clinical, radiological and pleural fluid biochemical findings for the accurate identification of exudative effusions (according to Light's criteria) secondary to HF, when natriuretic peptides are not immediately available. To this end, an easily applicable scoring model was devised and validated.

Section snippets

Study population

A retrospective review was done of the medical charts of all consecutive patients who were subjected to a diagnostic thoracentesis at the Arnau de Vilanova University Hospital (Lleida, Spain) from 1994 to 2016, and whose pleural fluids met Light's criteria for exudates [4]. This 450-bed tertiary care facility serves a population of approximately 450,000 people. Recruited patients from this hospital aided in the generation of a scoring system for discriminating between cardiac and non-cardiac

Patients characteristics

A total of 3182 adult patients with exudative pleural effusions, of which 276 (8.7%) were related to HF, composed the derivation sample. The validation sample was comprised of 1165 patients with a similar proportion of cardiac (107, 9.2%) and non-cardiac effusions (1058, 90.8%) as the derivation set (p = 0.60). Also, the median age and sex of cardiac and non-cardiac effusions were comparable between both cohorts. These and other baseline characteristics are displayed in Table 1, Table 2.

Diagnostic accuracy of individual findings for cardiac effusions (derivation set)

The

Discussion

This study presents a clinical scoring model for identifying patients with pleural effusions due to HF, which should only be applied when pleural fluids meet Light's criteria for exudates. This score exceeded the discriminative capabilities of what is routinely recommended in clinical practice, namely the protein and albumin gradients in isolation. Overall, the scoring system may represent a useful tool in the identification of cardiac pleural effusions miscategorized by standard criteria, when

Conclusions

We derived and validated a simple rule which should be viewed as a diagnostic weight to estimate the probability of HF in patients whose pleural fluids meet Light's criteria for exudate. A prospective validation of our results is warranted.

Specific author contributions

J.M.P. and L.F. had full access to all the data and take full responsibility for the integrity of the data and the accuracy of the data analysis. J.M.P. contributed to the design of the study, data interpretation and drafting the manuscript. L.F., C.C., L.V., A.E. and S.B. contributed to data acquisition. S.B. contributed to data analysis and interpretation. R.L. provided revision for important intellectual content. All authors approved the final version of the manuscript for publication.

Financial/nonfinancial disclosures

None declared.

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Authors have no conflict of interests to disclose.

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